A known control device, see for example German U 70 24 806, comprises a motor-driven hydraulic medium pump which can be connected via associated control valves to a medium reservoir and via pump branch lines to a chamber of a lifting cylinder and a locking cylinder of the loading tailgate. A pressure intensifier piston cylinder is connected in parallel to the pump branch lines.
According to an earlier proposal, see U.S. application Ser. No. 07/838,406, filed Mar. 3, 1992, by the inventor hereof, now U.S. Pat. No. 5,255,517, to which Austrian Patent No. 392,447 corresponds, an electric manometric or pressure switch by means of which the pump motor drive can be stopped when a predetermined pressure is exceeded, or an adjustable hydraulic valve by means of which the pump branch lines can be blocked or the pump line can be connected to a return line to the medium reservoir and possibly the pump motor drive can be stopped, is connected to the chamber of the smaller head end of the pressure intensifier piston cylinder connected to the locking cylinder.
By virtue of this device, the pump motor is stopped and/or the hydraulic medium supply line is blocked or unloaded in a constructionally simple manner before overload of the closing cylinder of the loading tailgate can occur.
According to an advantageous embodiment as disclosed in the earlier proposal, a counter for the number of cases where the pressure is exceeded can be activated by the electric manometric or pressure switch or by the adjustable hydraulic valve.